It is known to produce moulded parts for various applications, and having various shapes and configurations, by moulding materials including polymer resins, in particular for the manufacture of moulded parts composed of fibre reinforced resin matrix composite materials. Such composite materials are typically manufactured from moulding materials which may typically comprise, for example, (a) the combination of dry fibres and liquid resin, (b) prepregs and/or (c) panel moulding compounds (SMC). Other materials may also be present, such as sandwich core materials and surfacing layers for forming a desired surface finish on the moulded part.
Many products are moulded by a manual process of laying-up the moulding material into a one sided mould, which moulds a single side of the resultant moulded article. Other products require a two-sided moulding process. In order to provide high manufacturing tolerance to the two-sided moulded part, it is sometimes required to use a press-moulding process in which the moulding material is moulded in a closed mould under elevated pressure.
The tooling is rigid, and accordingly a hydraulic pressure within the resin material of the moulding material is needed to achieve full impregnation of the fibres by the resin and cause resin flow to fill the geometrical details within the mould cavity, particularly at the peripheral edges of the mould cavity. Hydraulic pressure in the resin is generated by the press closing on the preform.
It is known to use syntactic material in prepregs. For example, the Applicant incorporates a syntactic layer, incorporating glass microspheres, into a moulding material available in commerce under the trade name Sprint CBS. The glass microspheres lower the density and increase the specific flexural modulus of the resultant moulded product. SMC material is heavy and does not yield parts with a good surface finish.
Prepreg stacks are typically made from assembling stacks of impregnated unidirectional prepreg to form a multiple angle ply laminate. This is difficult to conform to the mould geometry and high pressure is needed to press these materials.